A microring resonator (MRR) has been used in various photonic devices due to the potentially large quality factor (Q) and small size of the MRR. Such devices have been used as the building blocks of integrated optical filters, switches, modulators, logic gates, memories, delay lines, sensors, and laser cavities.
The distributed Bragg reflector (DBR) is a technology that has enabled numerous optoelectronic devices including vertical cavity lasers, narrow linewidth lasers, fiber Bragg gratings, dichroic mirrors, and dispersion compensation filters. The DBR laser has many applications including communications, metrology, sensing, and spectroscopy.
A dispersive photonic bandgap crystal (PhC) in an MRR have been investigated for narrowing a resonator linewidth using enhanced modal dispersion near the PhC bandgap. The device was designed to have a sharp notch in reflection at resonance by coupling a PhC MRR to a broadband external linear reflective PhC in a bus waveguide. Good notch filtering performance requires that the external PhC be both highly reflective and have minimal scattering loss, and also requires precise phase matching of the PhC k-vector to the MRR. These constraints make fabrication of the device difficult. Also, when the PhC is very highly reflective, the strength of the field in the ring is approximately less than or equal to the input field strength in the bus waveguide.